Radio apparatus and adaptive array processing method

ABSTRACT

A correlator detects arriving timings of a desired wave and an interfering wave from a signal transmitted by the OFDM scheme. A reception response vector estimator estimates a first response vector for a signal arriving within a guard interval section from the head arriving wave and a second response vector for a signal arriving after the guard interval section from the head arriving wave out of the desired wave, and also a third response vector for a signal arriving within the guard interval section from the head arriving wave and a fourth response vector for a signal arriving after the guard interval section from the head arriving wave out of the interfering wave. An adaptive array block provides a weight vector based on a result of Fourier transform on the first to fourth response vectors.

TECHNICAL FIELD

The present invention relates to a configuration of a radio apparatusemployed in a base station and an adaptive array processing method inradio communication mainly for a mobile such as a cellular phone.

BACKGROUND ART

In the field of mobile communication systems (for example, personalhandyphone system: PHS) evolving rapidly these few years, an adaptivearray base station is adapted to practical usage. The adaptive arraybase station separates and extracts a signal of the desired wave byapplying the well known adaptive array processing on the receptionsignal of an array antenna composed of a plurality of antennas in orderto suppress the effect of interfering waves to obtain favorablecommunication quality.

Furthermore, by employing such an adaptive array base station, a PDMA(Path Division Multiple Access) system can be realized. The PDMA systemallows mobile terminal devices of a plurality of users to be subjectedto path division multiple access to a radio base system by dividing thesame time slot of the same frequency spatially in order to improve theusage efficiency of radio frequency. The PDMA system is also called theSDMA system (Space Division Multiple Access) system.

FIG. 11 represents the channel arrangement of the various communicationsystems of frequency division multiple access (FDMA), time divisionmultiple access (TDMA), and space division multiple access (SDMA).

First, FDMA, TDMA and SDMA will be described briefly with reference toFIG. 11. FIG. 11( a) corresponds to FDMA. The analog signals of users1-4 are subjected to frequency-division and transmitted over radio wavesof different frequencies f1-f4. The signals of respective users 1-4 areseparated by frequency filters.

FIG. 11( b) corresponds to TDMA. Digitized signals of respective usersare transmitted over radio waves at different frequencies f1-f4, andtime-divided for every prescribed period of time (time slot). Thesignals of respective users are separated by means of frequency filtersand time-synchronization between a base station and each mobile terminaldevice of respective users.

In the SDMA system shown in FIG. 11( c), the data of a plurality ofusers are transmitted with one time slot of the same frequency dividedspatially. In this SDMA, the signals of respective users are separatedby means of frequency filters, time-synchronization between a basestation and each mobile terminal device of respective users, and amutual interference canceller such as an adaptive array.

FIG. 12 is a schematic block diagram showing a configuration of atransmission and reception system 2000 of a conventional base stationfor SDMA.

In the configuration shown in FIG. 12, n antennas #1-#n (n: naturalnumber) are provided to establish identification between, for example, auser PS1 and a user PS2.

In a reception operation, the outputs of antennas are provided to an RFcircuit 2101 to be amplified by reception amplifiers, and thenfrequency-converted by a local oscillation signal. The converted signalshave the unnecessary frequency signal removed by filters, subjected toA/D conversion, and then applied to a digital signal processor 2102 asdigital signals.

Digital signal processor 2102 includes a channel allocation referencecalculator 2103, a channel allocating apparatus 2104, and an adaptivearray 2100. Channel allocation reference calculator 2103 calculates inadvance whether the signals from two users can be separated by theadaptive array. Based on the calculation result, channel allocatingapparatus 2104 provides channel allocation information including userinformation, selecting frequency and time, to adaptive array 2100.Adaptive array 2100 applies a weighting operation in real time on thesignals from antennas #1-#n based on the channel allocation informationto separate only the signal of a particular user.

[Configuration of Adaptive Array Antenna]

FIG. 13 is a block diagram showing a configuration of a transmission andreception unit 2100 a corresponding to one user in adaptive array 2100.The example of FIG. 13 has n input ports 2020-1 to 2020-n receiving thesignals from antennas #1-#n, respectively, to extract the signal of thedesired user from input signals of a plurality of users.

The signals input to input ports 2020-1 to 2020-n are applied via switchcircuits 2010-1 to 2010-n to a weight vector calculator 2011 andmultipliers 2012-1 to 2012-n.

Weight vector calculator 2011 calculates weight vectors w_(1i)-w_(ni)using input signals, a unique word signal that is the reference signalprestored in a memory 2014, and the output from an adder 2013. In thepresent specification, subscript “i” implies that the weight vector isemployed for transmission/reception with the i-th user. Therefore, theunique word signal is a training signal for adaptive array processing.

Multipliers 2012-1 to 2012-n multiply the input signals from input ports2020-1 to 2020-n by weight vectors w_(1i)-w_(ni), respectively. Themultiplied result is applied to adder 2013. Adder 2013 adds the outputsignals from multipliers 2012-1 to 2012-n to output the added signals asa reception signal S_(RX)(t). This reception signal S_(RX)(t) is alsoprovided to weight vector calculator 2011.

Transmission and reception unit 2100 a further includes multipliers2015-1 to 2015-n multiplying an output signal S_(TX)(t) of an adaptivearray radio base station by respective weight vectors w_(1i)-w_(ni)applied from weight vector calculator 2011. The outputs of multipliers2015-1 to 2015-n are applied to switch circuits 2010-1 to 2010-n,respectively. Specifically, switch circuits 2010-1 to 2010-n providesthe signals applied from input ports 2020-1 to 2020-n to a signalreceiver unit 1R in a signal receiving mode, and provides the signalfrom a signal transmitter unit 1T to input/output ports 2020-1 to2020-n.

[Operating Mechanism of Adaptive Array]

The operating mechanism of transmission and reception unit 2100 a ofFIG. 13 will be described briefly here.

For the sake of simplifying the description with reference to theequations, it is assumed that there are four antenna elements, and twousers PS effect communication at the same time. In such a case, signalsapplied to reception unit 1R from respective antennas are represented bythe equations set forth below.RX ₁(t)=h ₁₁ Srx ₁(t)+h ₁₂ Srx ₂(t)+n ₁(t)  (1)RX ₂(t)=h ₂₁ Srx ₁(t)+h ₂₂ Srx ₂(t)+n ₂(t)  (2)RX ₃(t)=h ₃₁ Srx ₁(t)+h ₃₂ Srx ₂(t)+n ₃(t)  (3)RX ₄(t)=h ₄₁ Srx ₁(t)+h ₄₂ Srx ₂(t)+n ₄(t)  (4)

Signal RX_(j) (t) represents a reception signal of the j-th (j=1, 2, 3,4) antenna. Signal Srx_(i) (t) represents a signal transmitted by thei-th (i=1, 2) user.

Coefficient h_(ji) represents the complex coefficient of a signal fromthe i-th user received at the j-th antenna, and n_(j) (t) represents thenoise included in the j-th reception signal.

The above equations (1)-(4) may be represented in vector form asfollows:X(t)=H ₁ Srx ₁(t)+H ₂ Srx ₂(t)+N(t)  (5)X(t)=[RX ₁(t), RX ₂(t), . . . , RX ₄(t)]^(T)  (6)H _(i) =[h _(1i) , h _(2i) , . . . , h _(4i)]^(T), (i=1, 2)  (7)N(t)=[n ₁(t), n ₂(t), . . . , n ₄(t)]^(T)  (8)

In equations (6)-(8), [ . . . ]^(T) denotes the transposition of [ . . .].

Here, X (t) represents the input signal vector, H_(i) the receptionresponse vector of the i-th user, and N (t) a noise vector.

The adaptive array antenna outputs as a reception signal S_(RX) (t) asynthesized signal obtained by multiplying the input signals fromrespective antennas by respective weight coefficients w_(1i)-w_(4i), asshown in FIG. 13.

Given these preliminaries, the operation of an adaptive array in thecase of extracting a signal Srx₁ (t) transmitted by the first user, forexample, is set forth below.

Output signal y1 (t) of adaptive array 2100 can be represented by thefollowing equations by multiplying input signal vector X(t) by weightvector W₁.y1(t)=X(t)W ₁ ^(T)  (9)W₁=[w₁₁,w₂₁,w₃₁,w₄₁]^(T)  (10)

In other words, weight vector W₁ is a vector with the weightcoefficients w_(j1) (j=1, 2, 3, 4) to be multiplied by the j-th inputsignals RXj (t) as elements.

Substituting input signal vector X (t) represented by equation (5) intoy1 (t) represented by equation (9) yields:y1(t)=H ₁ W ₁ ^(T) Srx ₁(t)+H ₂ W ₁ ^(T) Srx ₂(t)+N(t)W ₁ ^(T)  (11)

By a well known method, weight vector w₁ is sequentially controlled byweight vector calculator 2011 so as to satisfy the followingsimultaneous equations when adaptive array 2100 operates in an idealsituation.H₁W₁ ^(T)=1  (12)H₂W₁ ^(T)=0  (13)

If weight vector W₁ is perfectly controlled so as to satisfy equations(12) and (13), output signal y1 (t) from adaptive array 2100 iseventually represented by the following equations.y1(t)=Srx ₁(t)+N ₁(t)  (14)N ₁(t)=n ₁(t)w ₁₁ +n ₂(t)w ₂₁ +n ₃(t)w ₃₁ +n ₄(t)w ₄₁  (15)

Specifically, signal Srx₁ (t) emitted from the first of the two userswill be obtained for output signal y1 (t).

In FIG. 13, input signal S_(TX) (t) for adaptive array 2100 is appliedto transmitter unit 1T in adaptive array 2100 to be applied torespective one inputs of multipliers 2015-1, 2015-2, 2015-3, . . . ,2015-n. To the other inputs of these multipliers, weight vectors w_(1i),w_(2i), w_(3i), . . . , w_(ni) calculated by weight vector calculator2011 based on reception signals described above are copied and applied.

The input signals weighted by these multipliers are delivered tocorresponding antennas #1, #2, #3, . . . , #n via corresponding switches2010-1, 2010-2, 2010-3, . . . , 2010-n for transmission.

Identification of users PS1 and PS2 is made as set forth below. A radiowave signal of a cellular phone is transmitted in frame form. The radiowave signal of a cellular phone is mainly composed of a preamble formedof a signal series known to a radio base station, and data (voice andthe like) formed of a signal series unknown to the radio base station.

The preamble signal series includes a signal stream of information(unique word signal) to identify whether the current user is theappropriate user to converse for the radio base station. Weight vectorcalculator 2011 of adaptive array radio base station 1 compares theunique word signal output from memory 2014 with the received signalseries to conduct weight vector control (determine a weight coefficient)so as to extract the signal expected to include the signal seriescorresponding to user PS1.

The above description is based on a configuration in which the weightvector of the reception mode is copied to form the directivity of atransmission signal in a signal transmission mode. Alternatively, theweight vector of the reception mode can be corrected to be used as theweight vector for transmission taking into account the travel speed orthe like of the terminal device in a transmission mode.

As a communication system of high usage efficiency of frequency, theorthogonal frequency division multiplexing (OFDM) scheme is known.

The OFDM scheme is one type of multicarrier modulation of spreading dataof one channel into a plurality of carrier waves for modulation. In theOFDM scheme, the frequency spectrum of the signal employed incommunication is substantially rectangular.

FIG. 14 shows the extraction of three carriers (carrier waves) of thefrequency spectrum of a plurality of carriers employed in the OFDMscheme.

Attention is focused on the spectrum of one carrier wave shown in FIG.14. In the OFDM scheme, the frequency interval of a plurality of carrierwaves is set so that the zero point of the spectrum of this one carrierwave matches the frequency of an adjacent carrier wave. In other words,each carrier wave is arranged at a frequency avoiding mutualinterference, and each carrier wave is orthogonal to each other.

The interval Δf of the frequency of each carrier wave is expressed bythe following equation, where Ts is the duration of one symbol oftransmitted data.Δf=1/Ts×n (n: natural number)

FIG. 15 represents the waveform of the symbol transmitted in accordancewith the OFDM scheme.

As a result of combining the waveforms of i=1 to i=N carrier waves,i.e., a total of N carrier waves, a signal represented by the bottommost waveform in FIG. 15 is employed as the transmission symbol of OFDM.

In order to obtain each carrier component in the modulation of the OFDMscheme, inverse discrete Fourier transform is carried out on thebaseband signal. Correspondingly, in the demodulation process of areception wave, discrete Fourier transform is applied on the receptionsignal through the algorithm of the so-called Fast Fourier Transform(FFT).

In the OFDM signal waveform in FIG. 15, a “guard interval” is providedbefore the valid symbol period. Such a guard interval has a portion ofthe valid symbol waveform, for example a signal of a predetermined timeTg at the tail of the valid symbol waveform, copied and added.

The guard interval is provided as countermeasures against an interferingwave caused by multipath interference.

In the case where a desired wave and an interfering wave arriving behindtime are combined to form a reception signal, the effect of theinterfering wave is limited within the guard interval period if thedelay time of the interfering wave is within the time set as the guardinterval. By setting the guard interval period longer than the expecteddelay time of an interfering wave, demodulation can be performed withthe effect of an interfering wave removed.

FIG. 16 is a schematic diagram to describe a demodulation operation whensuch a desired wave and interfering wave are received.

In demodulation according to the OFDM scheme, a time window termed “FFTwindow” is provided in each symbol period, as shown in FIG. 16. Thistime window denotes the section corresponding to the process of cuttingout only the valid symbol section from the received OFDM transmissionsymbol. The FFT window is set equal to the valid symbol period lengthTs. The guard interval period is set longer than the delay time of aninterfering wave, as mentioned above. Accordingly, the orthogonality ofeach carrier wave of a reception wave can be maintained even if there isan interfering wave since a signal present in the guard interval periodis a signal in the same valid symbol. Thus, demodulation with the effectof such an interfering wave removed can be carried out at the receivingside.

It is expected that a higher communication quality and a receptionscheme of higher usage efficiency of radio frequency can be realized bythe combination of the above-described adaptive array scheme and OFDMscheme.

However, the mere combination of the two schemes will pose problems setforth below.

[Problem in Configuration of Operating Adaptive Array Differing forEvery Carrier]

An example of a first configuration for OFDM transmission using anadaptive array will be described hereinafter.

By such a configuration, the above-described multiple access of the SDMAscheme can be established by application of adaptive array technique.

FIG. 17 is a schematic block diagram to describe a configuration of suchan adaptive array base station 3000.

Referring to FIG. 17, it is assumed that adaptive array base station3000 conducts transmission and reception using an adaptive array antennaincluding four antennas #1-#4, for the sake of simplification. In FIG.17, description is based on a configuration directed to reception inaccordance with the configuration of an adaptive array base station.

Referring to FIG. 17, adaptive array base station 3000 includes an A/Dconverter 3010 receiving signals from adaptive array antennas #1-#4 tocarry out detection and analog-digital conversion, and an FFT unit 3020applying fast Fourier transform on a received digital signal from A/Dconverter 3010 to separate the signal for each carrier wave.

In the present description, the signal from the i-th antenna for thefirst carrier among the signals output from FFT unit 3020 is representedas signal f1, i (1, i: natural number).

Adaptive array base station 3000 further includes N (N: total number ofcarriers) adaptive array blocks 3030.1-3030.N provided for each carrier.Each adaptive array block receives the component of a correspondingcarrier obtained by applying Fourier transform on the signal fromantennas #1-#4 through FFT unit 3020 to carry out adaptive arrayprocessing.

It is to be noted that only adaptive array block 3030.1 for the firstcarrier is depicted in FIG. 17.

Adaptive array block 3030.1 includes, likewise the adaptive array basestation shown in FIG. 13, a reception weight vector calculator 3041receiving signals f1, 1-f1, 4 to calculate a reception weight vector,multipliers 3042-1 to 3042-4 receiving signals f1, 1 to f1, 4 atrespective one inputs and the reception weight vector from receptionweight vector calculator 3041 at respective other inputs, an adder 3043to receive and combine the outputs of multipliers 3042-1 to 3042-4, anda memory 3044 to prestore a unique word signal (reference signal) usedin the calculation of adaptive array processing by reception weightvector calculator 3041. Adder 3043 outputs a desired signal S1 (t) forcarrier 1. This desired signal S1 (t) is also applied to receptionweight vector calculator 3041.

By such a configuration, the signal from a desired user can be separatedfor each carrier from a signal transmitted by the OFDM transmissionscheme by adaptive array processing for reception.

In the configuration of such an adaptive array base station 3000, thefollowing problems are noted.

As described above, the signal of one channel is spread into a pluralityof carriers for transmission in the OFDM scheme.

Therefore, the number of symbols of a reference signal included for eachcarrier is often not sufficient for the signals transmitted through theOFDM scheme. For example, in “multimedia mobile access communicationsystems (MMAC) recommended by the Ministry of Public Management or thelike, two symbols are defined for the reference signal for each OFDMcarrier (subcarrier).

In this case, it will be difficult to converge the weight based on theconfiguration of adaptive array base station 3000 shown in FIG. 17.There was a problem that directivity of favorable accuracy could not beestablished.

Furthermore, the configuration of adaptive array base station 3000 shownin FIG. 17 has problem set forth below.

FIG. 18 is a schematic diagram representing the timing of a signalreceived at adaptive array base station 3000 of FIG. 17.

In FIG. 18, the section labeled “G” represents the above-described guardinterval period of a reception signal.

The primary desired wave is generally the first signal arriving at thebase station. The first arriving signal is referred to as “head arrivingsignal” hereinafter.

With respect to this head arriving signal, a signal arriving in delaywithin the guard interval period is called a “short delayed signal”whereas a signal arriving in delay for at least the guard intervalperiod from the head arriving signal is referred to as a “long delayedsignal”, under the influence of multipath. The route through which eachof a head arriving signal, a short delayed signal, and a long delayedsignal is transmitted is referred to as a “path”.

In FIG. 18, the signal sampling timing in adaptive array block 3030.1 isdenoted with an arrow.

Since adaptive array processing is carried out on a signal that has beendivided for each carrier in adaptive array base station 3000, thesampling timing of a signal is to be set at a time interval sufficientfor extracting a signal waveform for each carrier.

By adaptive array processing, a long delayed signal as shown in FIG. 18can be removed.

The bandwidth of a band-divided carrier is so narrow that a shortdelayed signal cannot be separated. Therefore, processing is carried outwith the head arriving signal and the short delayed signal regarded asthe same signal in adaptive array processing.

FIG. 19 shows the intensity distribution of signals corresponding torespective carriers after passing through such an adaptive array.

In each of frequencies f1-fN of carriers in FIG. 19, the spectrum of thehead arriving signal (head wave) and the spectrum of a short delayedsignal (short delayed wave) appear to be the same signal after theadaptive array processing, as mentioned above. However, since the bandfor the entire carriers is extremely wide, there may be the case wherethe head wave and the short delayed wave are opposite in phase in thecarrier indicated by the arrow in FIG. 19.

FIG. 20 represents the intensity distribution when the signals forrespective carriers are combined in the case of FIG. 19.

If adaptive array reception is conducted using a reference signal timedto the head wave, only a signal of small level can be extracted for thecarrier of a frequency having the head signal and the short delayedsignal in opposite phase. In other words, if adaptive array reception isconducted for each carrier, only a signal of an extremely low signallevel can be extracted for a carrier of a frequency that has the headwave and the short delayed wave in opposite phase, as shown in FIG. 19.

Since sufficient signal transmission cannot be conducted for the carrierindicated by the arrow in FIG. 19, a redundancy code must be used orcontrol must be provided to communicate without using this carrier. Thelatter is equivalent to remove as an unnecessary signal a signaloriginally arriving at the base station as a short delayed signal. Thiswill lead to degradation in reception sensitivity

Summarizing, there is a problem that is difficult to ensure a sufficientreference signal required for directional control of high accuracy inthe configuration of operating an adaptive array differing for eachcarrier as shown in FIG. 17.

There is also a problem that the reception sensitivity is degraded sincemultipath signals within the guard interval cannot be combined inmaximum ratio.

In other words, since a signal of a delay time within the guard interval(short delay component) has high correlation with the head signal, ashort delay component will be included in the array combined output ifcombining based on the adaptive array is carried out using a referencesignal timed to the head signal. However, in the case where a pluralityof carriers employed in communication are distributed over an extremelywide band in the OFDN scheme, there may be a case where the head waveand the short delayed wave are opposite in phase depending upon thecarrier. In such a case, there will be a problem that combination at themaximum ratio is not conducted when viewed over the entire carrier.

[Problems Based on a Configuration of Adaptive Array Operation withWeight to Entire Carrier]

In view of the above-described problems in the configuration of adaptivearray base station 3000, an approach of another configuration may beconsidered, conducting adaptive array processing on a signal prior toband-division by an FFT process.

FIG. 21 is a schematic block diagram to describe a configuration of anadaptive array base station 4000 operating an adaptive array,calculating a common weight for all the carriers.

Referring to FIG. 21, adaptive array base station 4000 includes,likewise adaptive array base station 3000 of FIG. 17, an A/D converter4010 applying detection and analog-digital conversion on signalsreceived from four antennas #1-#4, a reception weight vector calculator4041 receiving outputs of A/D converter 4010 to calculate receptionweight vectors for signals of respective antennas, multipliers 4042-1 to4042-4 receiving signals from array antennas at respective one inputs,and receiving weight vectors from reception weight vector calculator4041 at respective other inputs, an adder 4043 to receive and combineoutputs from multipliers 4024-1 to 4042-4, a memory 4044 to prestore areference signal employed in calculating weight vectors by receptionweight vector calculator 4041, and an FFT unit 4050 applying fastFourier transform processing on a received output from adder 4043 forseparating into signals S_(1(t))-S_(N(t)) of the desired waves forrespective carriers. The output from adder 4043 is applied to receptionweight vector calculator 4041 to be used in the calculation of areception weight vector.

FIG. 22 is a schematic diagram to describe an operation of adaptivearray base station 4000 of FIG. 21.

In FIG. 22, “G” denotes a guard interval period. For the purpose ofapplying adaptive array processing on a signal not yet subjected toband-division, the sampling timing of, for example, reception weightvector calculator 4041 in the adaptive array must be set shorter thanthat for a signal subjected to band division as shown in FIG. 18.

A long delayed signal can similarly be removed by adaptive arrayprocessing through an adaptive array block.

The signal applied to an adaptive array block has an extremely wide bandsince it is not band-divided. In other words, a head arriving signal anda short delayed signal will be recognized as completely differentsignals at reception weight vector calculator 4041. Therefore, suchshort delayed signals will be removed by adaptive array processing.

This operation is disadvantages in that, although the short delayedsignal per se is a desired wave whose property may be improved if usedeffectively, such a short delayed signal will be removed by the adaptivearray processing, resulting in the problem of degradation incommunication quality.

Furthermore, since a short delayed signal will be regarded as aninterfering signal, it will look as if a large number of interferingwaves are arriving when viewed on part of adaptive array base station4000. If directivity is established by the adaptive array in order toremove such signals, there is a possibility of no degree of freedom ofthe antenna left.

If there is no degree of freedom of antenna left, the gain towards thedirection of a desired wave will be degraded, or the interference maynot be completely removed since it will look as if there areinterference exceeding the antenna degree of freedom.

The present invention is directed to overcome the above-describedproblems. An object of the present invention is to provide an adaptivearray base station that can combine at the maximum ratio the multipathsignals within a guard interval to improve reception sensitivity even inthe case of adaptive array reception with respect to the OFDMtransmission scheme.

Another object of the present invention is to provide an adaptive arraybase station that can maintain the interference suppression performancewithout consuming the antenna degree of freedom in combining multipathsignals within a guard interval period.

DISCLOSURE OF THE INVENTION

In summary, a radio apparatus of the present invention for transmittingand receiving a signal transmitted with a guard interval section addedto each valid symbol section by an orthogonal frequency divisioncommunication scheme employing a plurality of carries includes: an arrayantenna having a plurality of antennas; arriving timing detection meansfor detecting an arriving timing of a desired wave from signals receivedby the array antenna; reception response vector estimation means forestimating a first response vector for a signal arriving within theguard interval section from a head arriving wave of the desired wave,and a second response vector for a signal arriving after the guardinterval section from the heard arriving wave of the desired wave; firstFourier transform means for applying Fourier transform on the first andsecond response vectors to extract components for respective ones of theplurality of carriers; second Fourier transform means for applyingFourier transform on reception signals from an array antenna to extractcomponents for respective carriers of reception signals for respectiveones of the antennas; and adaptive array processing means provided forevery respective ones of the plurality of carriers, each adaptive arrayprocessing means receiving a component of a corresponding carrier fromthe second Fourier transform means among components for carriers ofreception signals for respective ones of the antennas for extracting thecomponent of the corresponding carrier in the desired wave. The adaptivearray processing means provides a weight vector used to extract thecomponent of the corresponding carrier based on components forcorresponding carriers of at least first and second response vectorsfrom the first Fourier transform means.

Preferably, the arriving timing detection means detects the desired wavein accordance with a cross correlation between the reception signalprior to Fourier transform in the second Fourier transform means and areference signal including a training signal component corresponding tothe plurality of carriers exceeding a predetermined threshold value, foreach antenna.

Preferably, the reception response vector estimation means sets theresponse level to 0 in the first and second response vectors at a timeother than the arriving timing detected by the arriving timing detectionmeans.

Preferably, the adaptive array processing means provides a weight vectorused to extract the desired wave for the corresponding carrier by acorrelation matrix for each carrier, provided based on components forcorresponding carriers of the first and second response vectors.

Preferably, the arriving timing detection means detects an arrivingtiming of n (n: natural number, n≧1) interfering waves from a signalreceived from an array antenna; the reception response vector estimationmeans estimates third to (2n+1)th response vectors for signals arrivingwithin the guard interval section from each head arriving wave for eachof the n interfering waves, and fourth to (2n+2)th response vectors forrespective signals arriving after the guard interval section from eachhead arriving wave for each of said n interfering waves; the firstFourier transform means further applies Fourier transform on the thirdto (2n+2)th response vectors to extract a component for each of theplurality of carriers; and the adaptive array processing means providesa weight vector used to extract the component of the correspondingcarrier based on components for corresponding carriers of the first to(2n+2)th response vectors from the first Fourier transform means.

Further preferably, the arriving timing detection means detects thedesired wave and the interfering wave in accordance with a crosscorrelation between the reception signal prior to Fourier transform inthe second Fourier transform means and a reference signal including atraining signal component corresponding to the plurality of carriersexceeding a predetermined threshold value, for each antenna.

Preferably, the reception response vector estimation means sets aresponse level to 0 in the first to (2n+2)th response vectors at a timeother than the arriving timing detected by the arriving timing detectionmeans.

Preferably, the adaptive array processing means provides a weight vectorused to extract the desired wave for the corresponding carrier by acorrelation matrix for each carrier, provided based on components forcorresponding carriers of the first to (2n+2)th response vectors.

Preferably the adaptive array processing means provides a weight vectorused to extract the interfering wave for the corresponding carrier by acorrelation matrix for each carrier.

Preferably, the reception response vector estimation means estimates thefirst to (2n+2)th response vectors by the MMSE scheme.

According to another aspect of the present invention, an adaptive arrayprocessing method to extract a signal transmitted with a guard intervalsection added to each valid symbol section by an orthogonal frequencydivision communication scheme employing a plurality of carriers forevery component corresponding to the plurality of carriers by adaptivearray processing includes the steps of: detecting an arriving timing ofat least a desired wave from signals received by an array antenna havinga plurality of antennas; estimating a first response vector for a signalarriving within the guard interval section from a head arriving wave outof the desired wave, and a second response vector for a signal arrivingafter the guard interface section from the head arriving wave of thedesired wave; applying Fourier transform on the first and secondresponse vectors to extract components for respective ones of theplurality of carriers; providing a weight vector used to separate byadaptive array processing a component corresponding to the carrier for adesired wave, based on components for carriers of at least first andsecond response vectors; applying Fourier transform on reception signalsfrom the array antennas to extract carrier components of receptionsignals for respective antennas; and multiplying the weight vector bythe carrier component of a reception signal for each antenna to extractthe component of the corresponding carrier for the desired wave.

Preferably, the step of detecting an arriving timing further includesthe step of detecting the arriving timing of at least one interferingwave. The method further includes the steps of estimating a thirdresponse vector for a signal arriving within the guard interval sectionfrom the head arriving wave out of an interfering wave, and a fourthresponse vector for a signal arriving after the guard interval sectionfrom the head arriving wave out of the interfering wave; and applyingFourier transform on the third and fourth response vectors to extractcomponents for respective ones of the plurality of carriers. The step ofproviding a weight vector provides the weight vector based on componentsfor carriers of the first to fourth response vectors.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic block diagram showing a structure of adaptivearray base station 1000 according to an embodiment of the presentinvention.

FIG. 2 is a schematic diagram to describe a reception signal of adaptivearray base station 1000 shown in FIG. 1.

FIG. 3 is a schematic diagram to describe a configuration of a desiredwave S_(d) (t) and interfering wave S_(u) (t).

FIG. 4 is a schematic diagram to describe an operation of a correlator1030 in adaptive array base station 1000 of FIG. 1.

FIG. 5 represents the time dependency of a correlation functionρ_(n,d)(t).

FIG. 6 represents the time dependency of an absolute value component ofcross function ρ_(n,d)(t) of FIG. 5.

FIG. 7 shows the time change of a response ρ_(n, dd)(t) and a responseρ_(n,du)(t).

FIG. 8 represents a complex response ρ_(n,dd)(t), and a complex responseξ_(n,dd)(k) for each carrier obtained by fast Fourier transform thereon.

FIG. 9 is a first flow chart to describe an overall operation ofadaptive array base station 1000.

FIG. 10 is a second flow chart to describe an overall operation ofadaptive array base station 1000.

FIG. 11 shows an arrangement of a channel in each type of communicationsystem of frequency division multiple access, time division multipleaccess and spatial division multiple access.

FIG. 12 is a schematic block diagram showing a structure of atransmission and reception system 2000 of a conventional SDMA basestation.

FIG. 13 is a block diagram showing a configuration of a transmission andreception unit 2100 a corresponding to one user in adaptive array 2100.

FIG. 14 is an extraction of three carriers among the frequency spectrumof a plurality of carriers (carrier waves) employed in the OFDM scheme.

FIG. 15 represents a waveform of a transmission symbol transmitted bythe OFDM scheme.

FIG. 16 is a schematic diagram to describe a demodulation operation whena desired wave and an interfering wave are received.

FIG. 17 is schematic block diagram to describe a configuration of anadaptive array base station 3000.

FIG. 18 is a schematic diagram representing a timing of a signalreceived by adaptive array base station 3000 shown in FIG. 17.

FIG. 19 represents an intensity distribution of a signal correspondingto each carrier after passing through the adaptive array.

FIG. 20 represents an intensity distribution when signals of respectivecarriers are combined in the case shown in FIG. 19.

FIG. 21 is a schematic block diagram to describe a configuration of anadaptive array base station 4000.

FIG. 22 is a schematic diagram to describe an operation of adaptivearray base station 4000 of FIG. 21.

BEST MODE FOR CARRYING OUT THE INVENTION First Embodiment

FIG. 1 is a schematic block diagram to describe a configuration ofadaptive array base station 1000 according to an embodiment of thepresent invention. Adaptive array base station 1000 of the presentinvention transmits and receives a signal having directivity by adaptivearray processing with respect to a mobile station such as a user'sterminal. It is to be noted that adaptive array base station 1000 canalso transmit and receive a signal with respect to a mobile stationthrough the spatial division multiple scheme as will be describedafterwards.

Referring to FIG. 1, adaptive array base station 1000 includes an arrayantenna formed of n (n: natural number) antennas, an A/D converter 1010to conduct detection and analog-digital conversion on signals receivedfrom array antennas #1-#n, FFT units 1020.1-1020.n provided forrespective n antennas, receiving outputs from A/D converter 1010 toseparate and extract signals for respective carriers for correspondingantennas, a correlator 1030 receiving signals from A/D converter 1010 todetect arriving timings of a desired wave and an interfering wave, aswill be described afterwards, a memory 1040 to store reference signalscorresponding to the desired wave and the interfering wave in order todetect the arriving timings of the desired wave and the interfering waveat correlator 1030, a reception response vector estimator 1050 receivingsignals prior to fast Fourier transform, applied to correlator 1030 fromA/D converter 1010, and information on the arriving timing of a signaldetected at correlator 1030 for estimating a response vector in aprocedure that will be described afterwards for the desired wave and theinterfering wave, FFT units 1060.1-1060.n provided corresponding torespective antennas, receiving a reception response of each antennaestimated by reception response vector estimator 1050 and applying fastFourier transform to extract a response vector for each carrier, andadaptive array blocks 1070.1-1070.N (N is the total number of carriers)provided for respective carriers, receiving response vectors ofcorresponding carriers for antennas #1-#n from FFT units 1060.1-1060.nto apply adaptive array processing.

In FIG. 1, only adaptive array block 1070.k corresponding to the k-thcarrier is depicted.

Adaptive array block 1070.k includes a reception weight calculator1072.k calculating a weight vector, multipliers 1080-1 to 1080-nreceiving signals for the k-th carrier from FFT unit 1020.1-1020.n atrespective one input nodes and the weight vector from reception weightcalculator 1072.k at respective other input nodes, and an adder 1090receiving and adding the signals from multipliers 1080-1 to 1080-n tooutput a desired signal Sk (t) for the k-th carrier.

FIG. 2 is a schematic diagram to describe a reception signal of adaptivearray base station 1000 shown in FIG. 1.

In adaptive array base station 1000, the reception wave includes adesired wave S_(d) (t), a delayed wave S_(d) (t−τ_(S)) of the desiredwave, an interfering wave S_(u) (t), and a delayed wave S_(u) (t−τ_(i))of the interfering wave. In the present description, time τ_(s) and timeτ_(i) are the delayed time. The subscript “d” of a signal implies thesignal of a desired wave. The signal of an interfering wave isrepresented by the subscript “u”.

FIG. 3 is a schematic diagram to describe a configuration of desiredwave S_(d) (t) and an interfering wave S_(u) (t).

Desired wave S_(d) (t) includes, but not exclusively, a reference signalsection of two symbols (training signal section) at the beginning, and adata signal section continuous thereto, for example.

In the present description, reference signal d (t) is an inverse Fouriertransform version of the training symbol of an input signal aligned inthe frequency domain, and is a signal of a time domain.

Similarly, interfering wave S_(u) (t) includes a reference signalsection u (t) of two symbols at the beginning, and a data signal sectioncontinuous thereto, for example.

It is assumed that reference signal section d (t) of a desired wave is asignal differing from the reference signal section u (t) of aninterfering wave without losing universality.

Therefore, adaptive array base station 1000 can identify the mobilestation such as a user's terminal by such a different reference signals(training signals).

[Operation of Correlator]

FIG. 4 is a schematic diagram to describe an operation of correlator1030 of adaptive array base station 1000 shown in FIG. 1.

The signals applied to correlator 1030 include a head arriving signalS_(d) (t), a short delayed signal S_(d) (t−τ₂) arriving at a delay timeτ₂ shorter than the guard interval period, and a long delayed signalS_(d) (t−τ₃) arriving at a delay time τ₃ corresponding to at least theguard interval period for a desired wave, as well as a head arrivingsignal S_(u) (t), a short delayed signal S_(u) (t−τ₂) arriving at adelay time τ₂ shorter than the guard interval period, and a long delayedsignal S_(u) (t−τ₃) arriving at a delay time τ₃ corresponding to atleast the guard interval period for an interfering wave.

In adaptive array base station 1000, it is necessary to process a signalprior to FFT processing for the operation of correlator 1030. Therefore,correlator 1030 samples a reception signal at a sufficiently shortsampling timing to carry out signal processing prior to FFT processing.

Signal X_(n) (t) applied from antenna #n to correlator 1030 can berepresented by the following equation (16).x _(n)(t)=h _(n,1) s _(d)(t)+h _(n,2) s _(d)(t−τ ₂)+h _(n,3) s _(d)(t−τ₃)+ . . . +p _(n,1) s _(u)(t)+p _(n,2) s _(u)(t−τ ₂)+p _(n,3) s _(u)(t−τ₃)+ . . . +n _(n)(t)  (16)

In equation (16), h_(n,1) designates the response of the head wave(element of a response vector) of a desired wave received at the n-thantenna #n, and ρ_(n,1) designates the response of the head wave of aninterfering wave (multiple party in SDMA) received at the n-th antenna#n.

Similarly, coefficients h_(n,2) and h_(n,3) designate the response ofdelayed waves of a desired wave (element of response vector) received atthe n-th antenna #n. Coefficients ρ_(n,2) and ρ_(n,3) designate theresponse of delayed waves of an interfering wave (multiple party inSDMA) received at the n-th antenna #n.

As mentioned before, signal S_(d) (t) is a signal of a desired wave,whereas signal s_(u) (t) is a signal of an interfering wave (multipleparty in SDMA).

It is to be noted that the terms of the interfering wave will increasein equation (16) when there are more interference or multiple users.

Calculation of a correlation function ρ_(n,d) (t) between a receptionsignal X_(n) (t) of antenna #n and reference signal s_(d) (t) (t is areference signal section) of a desired wave, and a correlation functionρ_(n,u) (t) between a reception signal X_(n) (t) of antenna #n and areference signal s_(u) (t) (t is a reference signal section) of aninterfering wave yields the following equations.ρ_(n,d)(t)=h _(n,1)δ(t)+h _(n,2)δ(t−τ ₂)+h _(n,3)δ(t−τ ₃)+I_(d)(t)  (17)ρ_(n,u)(t)=p _(n,1)δ(t)+p _(n,2)δ(t−τ ₂)+p _(n,3)δ(t−τ ₃)+I_(u)(t)  (18)

There remains in correlation function ρ_(n,d) (t) between the referencesignal of a desired wave and the reception signal of antenna #n thecorrelation component between the desired wave and the reference signal,as well as a small correlation component I_(d) (t) between theinterfering wave and noise.

Similarly, there remains in correlation function ρ_(n,u) (t) between thereception signal of antenna #n and the reference signal of theinterfering wave the correlation component between the interfering waveand the reference signal as well as a small correlation component I_(u)(t) between the interfering wave and noise.

Such a correlation function ρ_(n,d) (t) or correlation function ρ_(n,u)(t) is also termed “sliding correlation”.

FIG. 5 represents the time dependence of such a correlation functionρ_(n,d) (t).

In practice, correlation function ρ_(n,d) (t) is a signal, which isactually a complex number whose absolute value and phase on the complexplane change over time. For the sake of simplification, FIG. 5 showsonly the component in a predetermined direction on the complex plane.

Referring to FIG. 5, correlation function ρ_(n,d) (t) includes a peak P1as the head arriving signal component. A peak P2 corresponding to theshort delayed signal component immediately succeeds peak P2.Furthermore, there is a peak P3 corresponding to the long delayed signalcomponent at a time behind peak P2 of the short delayed signalcomponent.

The same applies to correlation function ρ_(n,u) (t) for an interferingwave.

FIG. 6 represents the time dependency of the absolute value component ofcorrelation function ρ_(n,d) (t) shown in FIG. 8. In FIG. 6, value Vtindicates the threshold value used in the process that will be describedafterwards.

[Operation of Reception Response Vector Estimator]

Correlation function ρ_(n,d) (t) corresponds to the reception response(complex number) of a desired wave signal of the n-th antenna. Thenon-orthogonal component of noise and interference will remain in thecomplex response obtained by such correlation, leading to considerableerror. However, the arriving time of the head arriving signal and thedelay time of the arriving time of a delayed signal can be properlyobtained by such correlation function ρ_(n,d) (t).

In view of the foregoing, the procedure of obtaining more accurately thereception response of a wave from a desired user terminal and thereception response of a wave from an interfering user terminal using thedelay time obtained by correlation functions ρ_(n,d) (t) and ρ_(n,u) (t)is performed by reception response vector estimator 1050 according tothe steps set forth below.

(Step 1)

First, a threshold value Vt is preset for the absolute values |ρ_(n,d)(t)| and |ρ_(n,u) (t)| of the correlation functions shown in FIG. 6 topick up signals equal to or exceeding the threshold value. As thisthreshold value Vt, a predetermined value is selected, or a standardsuch as extracting a signal lower than the highest signal level by apredetermined value is employed.

(Step 2)

Then, the complex response is accurately estimated by the so-called MMSE(Minimum Mean Square Error) method with respect to the signals picked upin which the mean square error between the array output and referencesignal is taken as the minimum, as will be described hereinafter.

Attention is focused on one certain antenna. A signal traincorresponding to sampled reception signals of the certain antenna isrepresented as below, identified as vector X.X=[x₁, x₂, x₃, . . . ]^(T)  (19)

Although not particularly limited, the number of elements of such avector can be set to, for example, 64 samples or 128 samples.

Signals corresponding to an inverse Fourier transform on referencesignals of a desired wave are represented as sd₁, sd₂, sd₃, . . . .Assuming that the delayed signal of a desired wave arrives through apath k with a delay time of τ_(k), the reference signal for such adesired wave is represented as set forth below, corresponding to thevector formed of the above-described sampling values of receptionsignals.d_(k)=[□, □, . . . □, sd₁, sd₂, . . . ]^(T)  (20)

In equation (20), a plurality of elements represented as □ are present,corresponding in number to delay time τ_(k). For example, the value ofthe element represented as □ will include the component of an inverseFourier transform on the signal present in a guard interval, whenpresent, located before a reference signal.

Consider the case where there is one interference signal, for the sakeof simplification.

In a similar manner, the time series of elements corresponding to aninverse Fourier transform on the reference signals of an interferencesignal is represented as su₁, su₂, . . . . Assuming that the delayedsignal of an interfering wave arrives through a path k′ with the delaytime of τ_(k′), the time series of reference signals of the interferencesignal is represented as set forth below, corresponding to vector Xformed of sampling elements of a reception signal.u_(k′)=[□, □, . . . □, su₁, su₂, . . . ]^(T)  (21)

In the estimation of a response vector based on MMSE, it is assumed thatthere are a plurality of, for example three, paths k having a differentdelay time for the desired wave, and also a plurality of, for examplethree, paths k′ of an interfering wave.

Under the above-described terms, the process of obtaining the responsevector for the reception signal of, for example, the n-th antenna,corresponds to obtaining a response h_(k) and a response ρ_(k′) for thedesired wave and interfering wave, respectively, so as to minimize anevaluation function J₁ represented by the following equation (22).

$\begin{matrix}{J_{1} = {{{X - {\sum\limits_{k}\;{h_{k} \cdot d_{k}}} - {\sum\limits_{k^{\prime}}\;{p_{k^{\prime}} \cdot u_{k^{\prime}}}}}}}^{2}} & (22)\end{matrix}$

By defining matrix Q and vector a as equations (23) and (24),respectively, evaluation function J₁ is represented as equation (25).

$\begin{matrix}{Q = \begin{pmatrix}{{path}\; 1} & {{path}\; 2} & \cdots & {{path}\; k} & {{path}\; 1^{\prime}} & {{path}\; 2^{\prime}} & \cdots & {{path}\; k^{\prime}} \\{sd}_{1} & \square & \cdots & \square & {su}_{1} & \square & \cdots & \square \\{sd}_{2} & \square & \cdots & \square & {su}_{2} & \square & \cdots & \square \\{sd}_{3} & {sd}_{1} & \cdots & \square & {su}_{3} & {su}_{1} & \cdots & \square \\\vdots & {sd}_{2} & \cdots & \vdots & \vdots & {su}_{2} & \cdots & \vdots \\\vdots & \vdots & \vdots & \square & \vdots & \vdots & \vdots & \square \\\vdots & \vdots & \vdots & {sd}_{1} & \vdots & \vdots & \vdots & {su}_{1} \\\vdots & \vdots & \vdots & \vdots & \vdots & \vdots & \vdots & \vdots\end{pmatrix}} & (23) \\{a = \begin{pmatrix}h_{1} \\h_{2} \\\vdots \\p_{1} \\p_{2} \\\vdots\end{pmatrix}} & (24)\end{matrix}$J ₁ =∥X−Qa∥ ²=(X−Qa)^(H)(X−Qa)=X ^(H) X−X ^(H) Qa−a ^(H) Q ^(H) X+a ^(H) Q ^(H) Qa  (25)

Under the prerequisite of this evaluation function J₁ being minimum forvector a, vector a can be obtained as equation (26) by the steps setforth below.

${\begin{matrix}\begin{matrix}{{\frac{\partial}{\partial a}J_{1}} = {{\frac{\partial}{\partial a}\left( {X^{H}X} \right)} - {\frac{\partial}{\partial a}\left( {X^{H}{Qa}} \right)} - {\frac{\partial}{\partial a}\left( {a^{H}Q^{H}X} \right)} + {\frac{\partial}{\partial a}\left( {a^{H}Q^{H}{Qa}} \right)}}} \\{= {{0 - 0 - {2\; Q^{H}X} + {2\; Q^{H}{Qa}}} = 0}}\end{matrix} & (26)\end{matrix}\therefore a} = {\left( {Q^{H}Q} \right)^{- 1}Q^{H}x}$

Thus, the complex amplitude of each path for a desired signal and aninterference signal can be obtained.

The above-described procedure is based on the provision for the n-thantenna. This procedure is similarly carried out for other antennas toobtain the response of a desired wave and the interfering wave for eachantenna.

(Step 3)

Signals other than those picked up as having at least the thresholdvalue and having the complex response estimated are all set to thesignal level of 0.

Accordingly, the remaining noise and interfering component can beremoved.

(Step 4)

For a delayed time longer than the guard interval time, the complexresponse is set to 0. As to a signal of a complex response formed onlyof a component corresponding to a delayed wave within the guard intervaltime, the reception response of ρ_(n,dd) (t) is placed for a desiredwave whereas a reception response (correlation function) of ρ_(n,ud) (t)is placed for an interfering wave. The subscript “dd” denotes a signalwithin the guard interval for a desired wave. Subscript “ud” denotes asignal within the guard interval for an interfering wave.

(Step 5)

In a similar manner, for a delayed wave shorter than the guard intervaltime, all the complex responses are set to 0. A response with othercomplex response levels left is newly set as a response (correlationfunction) ρ_(n,du) (t) and a response (correlation function) ρ_(n,uu)(t) for a desired wave and an interfering wave, respectively.

The subscript “du” denotes a delayed wave longer than the guard intervaltime for a desired wave. Subscript “uu” denotes a delayed wave having adelay time longer than the guard interval time for an interfering wave.

The response for an interfering wave obtained as described abovecorresponds to the complex response for multiple user in SDMA.

FIG. 7 represents the time variation of response ρ_(n,dd) (t) andresponse ρ_(n,du) (t) calculated as described above.

There are three paths in FIG. 7. The signals from paths 1 and 2 for thehead arriving wave and the first delayed wave have arrived at the basestation within the guard interval length. The delayed wave correspondingto path 3 has arrived at adaptive array base station 1000 at an elapseof a delayed time of at least the guard interval time from the arrivingtime of the head wave.

Therefore, response ρ_(n,dd) (t) includes two peaks whereas responseρ_(n,du) (t) includes one peak.

Through the above procedure, a first response vector formed of theresponse of each antenna corresponding to response ρ_(n,dd) (t) and asecond response vector formed of the response of each antennacorresponding to response ρ_(n,du) (t) are provided for a desired wave.

The same applies for the response of an interfering wave. A thirdresponse vector formed of the response of each antenna corresponding toresponse ρ_(n,ud) (t) and a fourth response vector formed of theresponse of each antenna corresponding to response ρ_(n,uu) (t) areprovided.

In the case where there are m (m≧2) interfering waves, the same appliesfor the interfering wave of the m-th wave. The (2m+1)th response vectorformed of the response of each antenna corresponding to a complexresponse including only the component corresponding to a delayed wavewithin the guard interval period and the (2m+2)th response vector formedof the response of each antenna corresponding to a complex response leftwith only the component corresponding to a delayed wave after the guardinterval time are provided.

[Operation of FFT Units 1060.1-1060.n]

Thus, a response for each antenna is obtained at reception responsevector estimator 1050.

Then, FFT units 1060.1-1060.n perform the process set forth below.

Complex response ρ_(n,dd) (t) of a signal transmitted from a desiredterminal and arriving within the guard interval is subjected to fastFourier transform to be converted into a complex response ξ_(n,dd) (k)for each carrier, where k is the carrier number.

FIG. 8 shows complex response ρ_(n,dd) (t) and a corresponding complexresponse ξ_(n,dd) (k) for each carrier obtained by fast Fouriertransform.

A similar operation is carried out on all the antennas to calculate thecomplex response for each carrier of all the antennas. A response vectorwith the complex response of each carrier as an element is calculated.Furthermore, complex response ρ_(n,du) (t) is subjected to fast Fouriertransform to obtain complex response ξ_(n,du) (k) for each carrier.

Through the above process, a response vector d_(d) (k) for a signalarriving within the guard interval period for the k-th carrier, forexample, is represented by equation (27). In a similar manner, theresponse vector d_(u) (k) of the kth carrier from complex responseρ_(n,du) (t) of a signal arriving at a delay time of at least the guardinterval, transmitted from a desired terminal, is calculated by equation(28).d _(d)(k)=└ξ_(1,dd)(k), ξ_(2,dd)(k), . . . , ξ_(n,dd)(k)┘^(T)  (27)d _(u)(k)=└ξ_(1,du)(k), ξ_(2,du)(k), . . . , ξ_(n,du)(k)┘^(T)  (28)

In a similar manner, complex response ρ_(n,ud) (t) of a signaltransmitted from an interfering user (all connected users other than thedesired user in SDMA) and arriving within the guard interval issubjected to fast Fourier transform to be converted into a responseξ_(n,ud) (k) for each carrier. A response vector i_(d) (k) of the k-thcarrier of an interfering wave is calculated by equation (29).

In a similar manner, complex response ρ_(n,uu) (t) of a signal arrivingafter the guard interval period for an interfering wave is subjected tofast Fourier transform to be converted into a response ξ_(n,uu) (k) foreach carrier. A response vector i_(u) (k) for an interfering wavearriving at a delay time of at least the guard interval is representedby equation (30).i _(d)(k)=└ξ_(1,ud)(k), ξ_(2,ud)(k), . . . , ξ_(n,ud)(k)┘^(T)  (29)i _(u)(k)=└ξ_(1,uu)(k), ξ_(2,uu)(k), . . . , ξ_(n,uu)(k)┘^(T)  (30)

In the case where there are a plurality of interferences or multipleusers, such a response vector is calculated for each interfering wave ormultiple user.

[Operation of Reception Weight Calculator]

Based on the response vector of the k-th carrier for each antennaobtained by fast Fourier transform as described above, reception weightcalculator 1070.k calculates the reception weight vector for the k-thcarrier as set forth below.

The response vector d_(d) (k) of a desired wave of a delay time withinthe guard interval, the response vector d_(u) (k) of a desired wave of adelay time exceeding the guard interval, the response vector i_(d) (k)⁾of an interfering wave of a delay time within the guard interval, andthe response vector i_(u) (k) of an interfering wave with a delay timeexceeding the guard interval for the k-th carrier are obtained by FFTunits 1060.1-1060.n as below.d _(d)(k)=└ξ_(1,dd)(k), ξ_(2,dd)(k), . . . , ξ_(n,dd)(k)┘^(T)d _(u)(k)=└ξ_(1,du)(k), ξ_(2,du)(k), . . . , ξ_(n,du)(k)┘^(T)i _(d)(k)=└ξ_(1,ud)(k), ξ_(2,ud)(k), . . . , ξ_(n,ud)(k)┘^(T)i _(d)(k)=└ξ_(1,uu)(k), ξ_(2,uu)(k), . . . , ξ_(n,uu)(k)┘^(T)  (31)

From these signals, the correlation matrix R_(XX) ^((k)) of the k-thcarrier is obtained by equation (32), whereby the reception weightvector of a desired signal is calculated by equation (33).

Furthermore, the reception weight vector for a party of a multiplesignal in the case of SDMA is calculated by equation (34).R _(xx) ^((k)) =d _(d)*(k)d _(d)(k)^(T) +d _(u)*(k)d _(u)(k)^(T) +i_(d)*(k)i _(d)(k)^(T) +i _(u)*(k)i _(u)(k)^(T)+σ² I  (32)W _(d) ^((k)) =R _(xx) ^((k)−1) d _(d)*(k)  (33)W _(i) ^((k)) =R _(xx) ^((k)−1) i _(d)*(k)  (34)

In equation (32), σ² is a positive real number. This value may beobtained empirically, avoiding singularity of the correlation matrix.Alternatively, a value of thermal noise power of the system may beselected. I represents the unit matrix of n×n.

In the case there is no interfering wave, the term corresponding to theinterfering wave in equation (32) becomes 0. The reception weight vectorof a desired signal is also calculated by equation (33), even for only adesired wave.

FIGS. 9 and 10 are flow charts to describe the overall operation ofadaptive array base station 100.

Referring to FIG. 9, upon initiation of the process (step S100), thesliding correlation between the reception signal for each antenna of thearray antenna and the reference signal of a desired wave is taken incorrelator 1030 (step S102).

At correlator 1030, the sliding correlation between the reception signaland reference signal of an interfering wave for each antenna of thearray antenna is also obtained (step S104).

At reception response vector estimator 1050, a signal having theabsolute value of a correlation value exceeding a predeterminedthreshold value for a desired wave and a signal having an absolute valueof a correlation value exceeding the predetermined threshold value foran interfering wave are picked up (step S106, S108).

At reception response vector estimator 1050, the complex response forthe signals picked up is estimated by MMSE and the like for a desiredwave and an interfering wave (step S110). All the signals other than thesignals picked up are set to the signal level of 0 (step S112).

Then, at reception response vector estimator 1050, a reception responseρ_(n,dd) (t) for a desired wave and a reception response ρ_(n,ud) (t)for an interfering wave are obtained with the signal component of adelay time longer than the guard interval set to 0 (step S114).Reception response vector estimator 1050 also obtains a receptionresponse ρ_(n,du) (t) for a desired wave and a reception responseρ_(n,uu) (t) for an interfering wave with the signal component of adelay time shorter than the guard interval set to 0 (step S116).

Referring to FIG. 10, FFT units 1060.1-1060.n apply Fourier transform onreception response ρ_(n,dd) (t), reception response ρ_(n,ud) (t),reception response ρ_(n,du) (t) and reception response ρ_(n,uu) (t) toobtain the complex response of each carrier for each antenna (stepS118).

Accordingly, 1) a complex response vector d_(d) (k) for every carriercorresponding to a signal arriving with a delay within the guardinterval of the desired wave, 2) a complex response vector d_(u) (k) forevery carrier corresponding to a signal arriving with a delay exceedingthe guard interval of the desired wave, 3) a complex response vectori_(d) (k) for every carrier corresponding to a signal arriving with adelay within the guard interval of an interfering wave, and 4) a complexresponse vector i_(u) (k) for every carrier corresponding to a signalarriving with a delay exceeding the guard interval of the interferingwave are provided (step S120).

At reception weight calculator 1072.k, a correlation matrix R_(XX)^((k)) of the k-th carrier is provided, based on the calculated complexresponse vector. The weight vector for the k-th carrier is calculatedwith respect to a desired wave (step S122).

At multipliers 1080-1 to 1080-n and adder 1090, the signal of eachcarrier obtained by applying Fourier transform on the reception signalfrom each antenna in the array antenna is multiplied by the weightvector to extract the desired signal for the k-th carrier (step 124). Inthe SDMA scheme, the weight vector is obtained also for an interferingwave, if necessary, to extract an interfering wave.

Furthermore, by combining the components for each carrier, the signaltransmitted through the OFDM scheme can be demodulated. Thus, theprocessing ends (step S130).

The reason why a short delayed signal is combined without beingattenuated by the phase difference from the head arriving wave in theabove method may be due to an adaptive array operation being carried outso as to direct the beam to each of the head signal and short delayedsignal for every carrier since response vector d_(d) (k) for eachcarrier includes both the components of the head signal and shortdelayed signal.

Therefore, combination in opposite phase will not occur even if thecarrier frequency differs. Also, since there are four terms of asignificant signal component from the equation of a correlation matrixR_(XX) (k) (in the case where there is one interference), the consumeddegree of freedom is 3. Control in a complete null direction is allowedwith an antenna of, for example, 4 elements.

In the case where null control is to be conducted on all the signalswithout depending upon the above-described scheme, control to directnull to a short delay will also have to be provided. In this case, thedegree of freedom is insufficient for an antenna of 4 elements.Sufficient properties cannot be achieved.

Second Embodiment

In the first embodiment, a complex response of a desired signal and acomplex response of an interfering signal were obtained in accordancewith a method described with reference to equations (22)-(26) as anoperation of reception response vector estimator 1050.

In the case where there is no overlapping between the reference signalsection of a desired signal and the reference signal section of aninterfering signal, the method described in accordance with equations(22)-(26) does not exactly apply.

The second embodiment is directed to a method of obtaining a complexresponse of a desired signal and a complex response of an interferencesignal applicable even in such a case.

(Estimation of Response of Desired Signal)

To obtain the complex response of a desired signal, an evaluationfunction J₂ applied by the following equation (35) is employed. Unlessstated otherwise, the notations of the following equations are similarto those of equations (22)-(26).

$\begin{matrix}{J_{2} = {{{X - {\sum\limits_{k}\;{h_{k} \cdot d_{k}}}}}}^{2}} & (35)\end{matrix}$

A matrix Q′ and a vector h defined by the following equations (36) and(37), respectively, are to be used.

$\begin{matrix}{Q^{\prime} = \begin{pmatrix}{sd}_{1} & \square & \cdots \\{sd}_{2} & \square & \cdots \\{sd}_{3} & {sd}_{1} & \cdots \\\vdots & {sd}_{2} & \cdots \\\vdots & {sd}_{3} & \cdots \\\vdots & \vdots & \cdots \\\vdots & \vdots & \cdots\end{pmatrix}} & (36) \\{h = \begin{pmatrix}h_{1} \\h_{2} \\h_{3} \\\vdots \\\vdots \\\vdots \\\vdots\end{pmatrix}} & (37)\end{matrix}$

Equation (35) can be rewritten as below.J ₂ =∥X−Q′h∥ ²  (38)

Based on the prerequisite of being minimum for vector h, complexresponse h_(k) for a path k of a desired wave is obtained by thefollowing equation (39), likewise equation (26).h=(Q′ ^(H) Q′)⁻¹ Q′X  (39)

(Estimation of Response of Interfering Signal)

In obtaining a complex response of an interfering signal, an evaluationfunction J₃ applied by the following equation (40) is employed.

$\begin{matrix}{J_{3} = {{{X - {\sum\limits_{k^{\prime}}\;{P_{k^{\prime}} \cdot u_{k^{\prime}}}}}}}^{2}} & (40)\end{matrix}$

A matrix Q″ and a vector p defined by equations (41) and (42),respectively, are employed.

$\begin{matrix}{Q^{\prime} = \begin{pmatrix}{su}_{1} & \square & \cdots \\{su}_{2} & \square & \cdots \\{su}_{3} & {su}_{1} & \cdots \\\vdots & {su}_{2} & \cdots \\\vdots & {su}_{3} & \cdots \\\vdots & \vdots & \cdots \\\vdots & \vdots & \cdots\end{pmatrix}} & (41) \\{p = \begin{pmatrix}p_{1} \\p_{2} \\p_{3} \\\vdots \\\vdots \\\vdots \\\vdots\end{pmatrix}} & (42)\end{matrix}$

Equation (40) is rewritten as below.J ₃ =∥X−Q″p∥ ²  (43)

Based on the prerequisite of being minimum for vector p, a complexresponse p_(k)′ for a path k′ of an interfering wave is obtained by thefollowing equation (44).p=(Q″ ^(H) Q″)⁻¹ Q″X  (44)

Advantages similar to those of the first embodiment can be providedthrough reception response vector estimator 1050 performing theabove-described estimation method of a complex response.

As described above, usage of a configuration of an adaptive array basestation of the present invention allows a multipath signal within aguard interval to be combined at the maximum ratio to maximize thereception sensitivity. Furthermore, the antenna degree of freedom is notconsumed when a multipath signal within the guard interval is combined.The interference suppression performance can be maintained.

INDUSTRIAL APPLICABILITY

According to a radio apparatus and adaptive array processing method ofthe present invention described above, the reception sensitivity can beimproved even in the case of adaptive array reception for the OFDMtransmission scheme. The present invention is particularly useful in anadaptive array base station.

1. A radio apparatus to transmit and receive a signal transmitted with aguard interval section added to each valid symbol section by anorthogonal frequency division communication scheme employing a pluralityof carriers, comprising: an array antenna including a plurality ofantennas, arrival timing detection means for detecting an arrivingtiming of a desired wave from signals received by said array antenna,reception response vector estimation means for estimating a firstresponse vector for a signal arriving within said guard interval sectionfrom a head arriving wave out of said desired wave, and a secondresponse vector for a signal arriving after said guard interval sectionfrom the head arriving wave out of said desired wave, first Fouriertransform means for applying Fourier transform on said first and secondresponse vectors to extract components for respective ones of saidplurality of carriers, second Fourier transform means for applyingFourier transform on reception signals from said array antenna toextract components for respective carriers of reception signals ofrespective ones of said antenna, and adaptive array processing meansprovided for respective ones of said plurality of carriers, eachadaptive array processing means receiving a component of a correspondingcarrier from said second Fourier transform means among components forcarriers of reception signals for respective ones of said antennas forextracting the component of the corresponding carrier in said desiredwave, wherein said adaptive array processing means provides a weightvector used to extract said component of the corresponding carrier basedcomponents for corresponding carriers of at least said first and secondresponse vectors from said first Fourier transform means.
 2. The radioapparatus according to claim 1, wherein said arriving timing detectionmeans detects said desired wave in accordance with a cross correlationbetween said reception signal prior to Fourier transform in said secondFourier transform means and a reference signal including a trainingsignal component corresponding to said plurality of carriers exceeding apredetermined threshold value, for every said antenna.
 3. The radioapparatus according to claim 1, wherein said reception response vectorestimation means sets a response level to 0 in said first and secondresponse vectors at a time other than said arriving timing detected bysaid arriving timing detection means.
 4. The radio apparatus accordingto claim 1, wherein said adaptive array processing means provides aweight vector used to extract said desired wave for said correspondingcarrier by a correlation matrix for each said carrier, provided based oncomponents for corresponding carriers of said first and second responsevectors.
 5. The radio apparatus according to claim 1, wherein saidarriving timing detection means detects an arriving timing of n (n:natural number, n≧1) interfering waves from a signal received from saidarray antenna, said reception response vector estimation means estimatesthird to (2n+1)th response vectors for signals arriving within saidguard interval section from each head arriving wave for each of said ninterfering waves, and fourth to (2n+2)th response vectors forrespective signals arriving after said guard interval section from eachsaid head arriving wave for each of said n interfering waves, said firstFourier transform means applies Fourier transform on said third to(2n+2)th response vectors to extract a component for each of saidplurality of carriers, and said adaptive array processing means providesa weight vector used to extract said component of the correspondingcarrier based on components for corresponding carriers of said first to(2n+2)th response vectors from said first Fourier transform means. 6.The radio apparatus according to claim 5, wherein said arriving timingdetection means detects said desired wave and said interfering wave inaccordance with a cross correlation between said reception signal priorto Fourier transform in said second Fourier transform means and areference signal including training signal component corresponding tosaid plurality of carriers exceeding a predetermined threshold value,for every said antenna.
 7. The radio apparatus according to claim 5,wherein said reception response vector estimation means sets a responselevel to 0 in said first to (2n+2)th response vectors at a time otherthan said arriving timing detected by said arriving timing detectionmeans.
 8. The radio apparatus according to claim 5, wherein saidadaptive array processing means provides a weight vector used to extractsaid desired wave for said corresponding carrier by a correlation matrixfor each said carrier, provided based on components for correspondingcarriers of said first to (2n+2)th response vectors.
 9. The radioapparatus according to claim 8, wherein said adaptive array processingmeans provides a weight vector used to extract said interfering wave forsaid corresponding carrier by a correlation matrix for each saidcarrier.
 10. The radio apparatus according to claim 5, wherein saidreception response vector estimation means estimates said first to(2n+2)th response vectors by an MMSE method.
 11. An adaptive arrayprocessing method to extract a signal transmitted with a guard intervalsection added to each valid symbol section by an orthogonal frequencydivision communication scheme employing a plurality of carriers forevery component corresponding to said plurality of carriers by anadaptive array processing, said method comprising the steps of:detecting an arriving timing of at least a desired wave from signalsreceived by an array antenna including a plurality of antennas,estimating a first response vector for a signal arriving within saidguard interval section from a head arriving wave out of said desiredwave, and a second response vector for a signal arriving after saidguard interval section from the head arriving wave out of said desiredwave, applying Fourier transform on said first and second responsevectors to extract components for respective ones of said plurality ofcarriers, providing a weight vector used to separate by adaptive arrayprocessing a component corresponding to said carrier for a desired wave,based on components for carriers of at least said first and secondresponse vectors, applying Fourier transform on reception signals fromsaid array antennas to extract carrier components of reception signalsfor respective ones of said antennas, and multiplying said weight vectorby said carrier component of a reception signal for each said antenna toextract the component of said corresponding carrier for said desiredwave.
 12. The adaptive array processing method according to claim 11,wherein said step of detecting an arriving timing further includes thesteps of detecting an arriving timing of at least one interfering wave,further comprising the steps of estimating a third response vector for asignal arriving within said guard interval section from the headarriving wave out of said interfering wave, and a fourth response vectorfor a signal arriving after said guard interval section from the headarriving wave out of said interfering wave, and applying Fouriertransform on said third and fourth response vectors to extractcomponents for respective ones of said plurality of carriers, whereinsaid step of providing a weight vector provides said weight vector basedon components for carriers of said first to fourth response vectors.